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23 posts

Geek
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Topic # 84408 30-May-2011 17:20
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Hi all, Apologies for the long story here! Skip to the end for the diagnosis but the background may be interesting to some..

As part of my Broadcasting work I have recently been using the 2degrees Huawei USB Modem with a Laptop for some Audio streaming projects.
While the throughput and even latency was great, the link was experiencing frequent audio pops and clicks, and other artifacts suggesting buffer under/overruns or lost packets..

I figured I was just pushing things a bit too much for a mobile network, We were running only 0.5 sec buffers each way in order to do a studio interactive outside broadcast (at 128kbps mp3)

Anyway, last Friday I set things up for a one way stream allowing decent buffering and AC3 encoding thinking all would be great..  Well it wasn't to be, and after a while I realised that there were still lots of Audio glitches happening!

To try and get to the bottom of the problem I first swapped to my XT modem without restarting the Laptop as broadcast time was nearing, same thing!
Hurredly installing mp3directcut for a test recording showed that the glitches were actually on the windows audio capture not the internet stream at all! Not only that but they were present on several different audio devices, external USB and internal, A frenzy of disabling devices and drivers ensued to no effect.. This was on a clean install of XP pro, so I had to think it was some recent laptop hardware failure.

Finally I used my own Windows7 laptop, installed the software and everything was fine for the night.

The next day I Investigated the problem and soon found that all windows WDM audio, in and out, glitched as soon as the 2degrees application launched. It didnt need to be connected or have the USB modem connected.
When I had previously tested with the XP modem the 2degrees App was left running from the previous connection..

I found that any time the 2degres Application is running, services.exe uses 15-20% processor time.
Using process monitor I tracked this down to it making 10-20,000 registry requests every second!
(I guess part of this was kernel time that was shared with the windows audio drivers causing my problem..)
Anyway the App is well behaved under Windows7 making only occasional registry access, and on two other XP machines the same bad behaviour occurs so I assume it is a bug!
The version is 2degrees Mobile Broadband 21.003.27.02.723.
Huawei dont seem to make updates directly available and I didn't fancy trying to explain it to the helpdesk, maybe someone here will be aware of this or be able to pass it on to Huawei, or is there a newer version?

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Uber Geek
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2degrees

  Reply # 476115 31-May-2011 10:27
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Thanks for the feedback.

We're trying to replicate your scenario. Can I ask does it happen if you use a dial up connection?

^POB



23 posts

Geek
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  Reply # 476133 31-May-2011 11:00
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Oh great, Thanks for looking into it..
 
I've just tested, and creating a dialup networking connection only there are no problems at all, and no sign of any unusual system activity..

193 posts

Master Geek


  Reply # 476179 31-May-2011 12:47
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My first thought is that 500ms is too low even if you are going for 'interactive' broadcast.

AFAIK, public radio uses a standard 7 second delay. (this is also to allow for censorship)

I would not necessarily expect consistent throughput through a wireless connection of any sort....So with 500ms you are not allowing much time for it to catch up if there is an interuption.....

True test would be to run ping -t while broadcasting if your latency spikes before or around the same time then you'd need to increase the buffer time by the however long the spike lasts for (and then some)



23 posts

Geek
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  Reply # 476200 31-May-2011 13:30
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This was experimental and Actually I'm really impressed with the network performance!.. I was running pings and seeing occasional spikes to around 200ms which I think is pretty good for a mobile network and portable device..  certainly couldn't guarantee it though :)

We do a lot of these over DSL now, the low delay is needed for conversations with the studio and other contributors, if realtime isn't needed I'll usually run about a 6 sec buffer for TCP.. Generally works pretty well, and the odd, but very rare, dropout is the tradeoff for low cost and anytime use.


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